This invention relates to electronic musical instruments and, in particular, to electro-acoustic guitars using a piezoelectric element to detect the vibrations of the guitar strings.
Electric guitars can be broadly divided between those having a solid guitar body and those having a hollow body, the latter being constructed essentially identically to an acoustic guitar except for the addition of a transducer to convert the vibrations of the strings into an electrical signal. The transducer in an electro-acoustic guitar is typically a piezoelectric element coupled to the strings at the junction of the strings with the body of the guitar. In a guitar with a solid body, the transducer is typically magnetic and is located near the junction of the strings with the body of the guitar.
Despite some superficial similarities, the two types of guitars serve distinctly different purposes and are actually quite distinct instruments. Generally, one wants the amplifier for an electro-acoustic guitar to reproduce the sounds of an acoustic guitar faithfully. A guitar with a solid body is generally coupled to an amplifier for producing varying kinds and amounts of distortion to the electrical signal from the magnetic transducer. Thus, an electro-acoustic guitar is itself a musical instrument whereas the combination of an electric guitar and an amplifier is the instrument.
A problem with electro-acoustic guitars is the piezo-electric transducer. The amplitude of the electrical signal from the transducer is a non-linear function of stress and frequency. Thus, a passage strummed softly sounds different from the same passage strummed vigorously. For years, musicians have adjusted the gain of amplifiers to match the expected playing level. If a piece included both loud and soft passages, the musician tried to find an intermediate setting that best accommodated both ends of the range. Usually the results were unsatisfactory, with soft passages sounding muffled and loud passages sounding too "bright." Simply providing automatic gain control, with or without high frequency roll-off, has not solved the problem.
It is known in the art to use a variable depth filter for reducing sibilance in audio recording and broadcast. These circuits typically include high frequency roll-off and are known as "de-essing" circuits. Attenuation of high frequencies is typically obtained by inverting or phase shifting 180.degree. the high frequency components and combining the inverted components with the original signal.
In view of the foregoing, it is therefore an object of the invention to provide a compensation circuit for the piezoelectric transducer in an electro-acoustic guitar.
Another object of the invention is to provide a compensation circuit for enabling an amplifier to faithfully reproduce the sound of an acoustic guitar.
A further object of the invention is to eliminate manual tuning or manual adjustment of an amplifier for an electro-acoustic guitar.